Meconium Aspiration Syndrome: Overview and Practice Questions

Meconium aspiration syndrome is a serious condition in newborns that results in severe respiratory distress. It occurs when the infant inhales a mixture of meconium and amniotic fluid during delivery.

In this article, we will provide an overview of meconium aspiration syndrome, including its causes, symptoms, and treatment options.

What is Meconium Aspiration Syndrome?

Meconium aspiration syndrome is a serious respiratory disorder that can occur in newborns when meconium is aspirated into the lungs.

Meconium is a sticky substance that is present in the intestines of all fetuses. It is normally passed during the first few days after birth. However, if the fetus is in distress, meconium can be passed into the amniotic fluid.

If the infant inhales a mixture of meconium and amniotic fluid during delivery, it can result in respiratory distress and breathing problems.

Causes

Meconium aspiration syndrome can be caused by a variety of factors, including:

• Fetal stress
• Post-term pregnancy
• Decreased oxygen to the infant
• Difficult labor
• Infection
• Diabetes in the pregnant mother
• Hypertension in the pregnant mother

Fetal stress is the primary cause of meconium aspiration syndrome. Stressful conditions can cause the fetus to pass meconium, resulting in health problems for the infant.

Symptoms

Meconium aspiration syndrome can cause a variety of symptoms in newborns, including:

• Respiratory distress
• Coughing
• Wheezing
• Rapid breathing
• Retractions
• Hypoxemia
• Cyanosis
• Tachycardia
• Low Apgar scores

Respiratory distress is the most common symptom of meconium aspiration syndrome and can range from mild to severe. It can be life-threatening in severe cases.

Treatment

Meconium aspiration syndrome is a serious condition that requires immediate medical intervention. Some treatment options include:

• Oxygen therapy
• Airway suctioning
• Intubation
• Mechanical ventilation
• Antibiotics
• Extracorporeal membrane oxygenation (ECMO)

Immediately after delivery, meconium should be suctioned from the infant’s upper airway. If the infant continues to show signs of hypoxemia after oxygen therapy has been administered, intubation and mechanical ventilation may be required.

In severe cases, ECMO may be necessary. This is a life-support measure that oxygenates the blood outside of the body and is often used as a last resort.

Pathophysiology of Meconium Aspiration Syndrome

Hypoxemia during utero leads to gut paralysis, which relaxes the anal sphincter causing meconium to pass. Then, when the hypoxic fetus gasps, thick meconium fluid is inhaled into the airways.

Meconium allows the air to enter the lungs; however, it inhibits the exhalation of carbon dioxide, which can result it a pneumothorax. Meconium also acts as an irritant, which can cause an infection that leads to an increased body temperature.

Meconium breaks down surfactant and causes impaired gas exchange. This causes blood to be shunted away from fetal circulation due to increased pulmonary resistance.

Meconium Aspiration Syndrome Practice Questions:

1. What is meconium aspiration syndrome?
It is a common cause of neonatal respiratory pathology characterized by in utero or perinatal aspiration of meconium-stained amniotic fluid that causes respiratory distress. It is a respiratory difficulty found in term and preterm infants with clinical features include tachypnea, nasal flaring, and grunting and chest retractions.

2. What is the abbreviation for meconium aspiration syndrome?
MAS.

3. What are the characteristics of meconium aspiration syndrome?
Increased temp (sign of infection) and signs of respiratory distress (nasal flaring, grunting, tachypnea, chest retractions).

4. What are the risk factors for meconium aspiration syndrome?
Thick/moderate fresh MEC liquor (requires consultation), late preterm and term babies increased risk, SGA/IUGR babies, post-term babies, post-dates, SGA, placental insufficiency, cord compression, fetal distress, small for gestational age, and the mother is obese and breech position birth.

5. Is Meconium Aspiration Syndrome more likely to affect preterm or post-term infants?
It is more likely to occur in post-term infants.

6. What are the tests and assessments required to establish meconium aspiration syndrome?
Ensure PAEDS at delivery, resuscitation equipment is available, assess for the need for suction at birth (if infant not breathing), vitals needs to be checked (T, RR, HR), BGLs, SpO2, access color, tone, reflexes and keep warm.

7. What are the risk factors of post-birth meconium aspiration syndrome exposure?
Respiratory distress, cold stress, weight loss, jaundice, and infection.

8. What is the epidemiology of deliveries associated with meconium aspiration syndrome?
13% of all deliveries are associated with MSAF and 5-12% of neonates delivered through MSAF develop meconium aspiration syndrome.

9. What are the clinical manifestations of meconium aspiration syndrome?
Meconium staining of nails, skin, umbilical cord, and placenta. Respiratory exam: initial respiratory depression followed by tachypnea, retractions, grunting, flaring, prolonged expiratory phase, rales, rhonchi, barrel chest with increased anteroposterior diameter, and cyanosis. Neurologic depression may be present. It also includes apnea, intercostal retraction, barrel chest and expiratory grunting.

10. What are the diagnostics for meconium aspiration syndrome?
Chest x-ray, arterial blood gas, and pre/post ductal pulse oximetry.

11. What can be seen on the chest x-ray in meconium aspiration syndrome?
Coarse, streaky, nodular pulmonary densities, often distributed asymmetrically, hyperinflation with flattening of the diaphragm, possible pneumothorax, pneumomediastinum, pleural effusion, cardiomegaly (secondary to hypoxia), irregular densities throughout the lungs with atelectasis and consolidation.

12. What can be seen on the ABG results in meconium aspiration syndrome?
Acute alveolar hyperventilation with hypoxemia (respiratory alkalosis from hyperventilation).

13. What can be seen on pre and postductal oximetry?
Used to evaluate right to left shunting through a patent ductus arteriosus (PDA) and difference in saturation of >5% suggests PPHN is present.

14. What are perinatal interventions for meconium aspiration syndrome?
Amnioinfusion, intrapartum suctioning of oropharynx and the perineum by the OB as soon as head is visible is no longer recommended as it does not prevent or alter the course of MAS, and tracheal intubation and suctioning to remove meconium from the airway for “depressed” neonates before stimulation and initiation of positive pressure in the delivery room.

15. What are the pathological/structural changes associated with meconium aspiration syndrome?
Partially obstructed airways, air trapping, alveolar hyperinflation; pulmonary air leaks; total obstructed airways and absorption atelectasis; Edema of the bronchial mucosa and alveolar epithelium; excessive bronchial secretions; alveolar consolidation; and, disrupted pulmonary surfactant production.

16. Can meconium aspiration by itself cause infection?
No, meconium is sterile.

17. How does meconium aspiration cause hypoxia?
Airway obstruction, interference with surfactant, chemical pneumonitis (bile acids, etc.), pulmonary HTN and good culture medium.

18. What are some risk factors for meconium aspiration?
Fetal distress and post-maturity.

19. What are the signs of meconium aspiration?
Respiratory distress and cord, skin and nails stained with meconium.

20. How can we manage meconium aspiration syndrome?
Give oxygen, IV fluids, appropriate feeding and antibiotics.

21. What is the heart rate of patients with meconium aspiration syndrome?
Tachycardia and elevated BP.

22. What is the secondary assessment for MAS?
Chest x-ray and ABG.

23. What is the treatment and management for meconium aspiration syndrome?
Suction the nasopharynx and oropharynx thoroughly when amniotic fluid is stained, stabilize and transfer to ICU, vigorous pulmonary hygiene, oxygen therapy, mechanical ventilation, and drug therapy (antibiotics and steroids).

24. How often is meconium present in births >34-40 weeks?
8-20%

25. How often is there meconium present in births >40-42 weeks?
30%.

26. Is meconium rare in babies < 34-40 weeks?
Yes, most likely an infection if present likes listeria.

27. When may meconium aspiration occur?
If the baby gasps in utero in pregnancy or labor or if there is meconium in the baby’s mouth when they take their first gasp at birth may go into the upper respiratory tract.

28. Is meconium always a sign of a problem?
No.

29. How much does inhaling meconium contribute to perinatal mortality?
2%.

30. What is the most important to be done by the respiratory therapist assisting in the delivery room with the newborn infant has aspirated meconium?
Suction out the meconium.

31. What do babies with meconium aspiration syndrome look like?
Their skin is stained green, the baby may appear limp with a low Apgar score, breathing may be rapid, labored or absent, the baby may be post-mature, peeling skin, no vernix and fetal bradycardia may have occurred in labor.

32. What are four main pulmonary effects that meconium aspiration can cause?
Airway obstruction, surfactant dysfunction, chemical pneumonitis and persistent pulmonary hypertension.

33. What is the effect of airway obstruction?
Airway collapses around the inhaled meconium. This causes increased resistance on exhalation, with hyperinflation of lungs due to trap gas resulting to pneumothorax (rupture/collapse of lung).

34. How does meconium cause surfactant dysfunction?
Free fatty acids have a higher minimal surface tension than surfactant. Surfactant gets stripped from the alveolar. Results in generalized atelectasis, partial collapse or incomplete inflation of the lung.

35. How does meconium cause chemical pneumonitis?
Enzymes, fats and bile salts in meconium cause irritation in airway and alveoli. The chemical response may cause pneumonitis within a few hours of aspiration.

36. How does meconium cause persistent pulmonary hypertension?
All the effects of meconium cause significant ventilation to perfusion mismatch.

37. What is the ongoing treatment of vigorous baby with meconium aspiration?
Stay with mum with close observation 24 hours.

38. What observations should be considered?
AC temperature and respiration, note general wellbeing, feeding and blood glucose.

39. What is the ongoing treatment for babies with thick meconium?
Seen by neonatologist one hour after birth.

40. What is the ongoing treatment for compromised babies with meconium aspiration?
Mec in the trachea, baby required significant resuscitation i.e. IPPV for more than a few minutes, cord pH<7.2, signs respiratory distress and will be admitted to NNU.

41. What is the treatment for meconium aspiration?
O2 to maintain SpO2 at >95%, CPAP, antibiotics and CXR if tachypnea or RD.

42. What are the complications from meconium aspiration?
Infection, pneumothorax (MAS is an air trapping condition so can occur at any time from birth), respiratory failure (may occur due to obstruction, inflammation, infection or shunting) and persistent pulmonary hypertension.

43. What may occur from aspiration of meconium?
Ball valve effect, atelectasis, total airway obstruction, alveolar hyperinflation and chemical pneumonitis.

44. What is associated with meconium aspiration syndrome when a ball valve effect is present?
Increased FRC.

45. What percentage of the infants with meconium aspiration syndrome requiring mechanical ventilation will likely develop a pneumothorax?
10-15%.

46. When a fetus experiences hypoxemia, it is at risk for which pulmonary complication?
Meconium aspiration.

47. What group is at the greatest risk for having meconium aspiration syndrome?
Post-term infants.

48. What can occur in infants with confirmed aspirated meconium?
Persistent pulmonary hypertension of the neonate (PPNH), chemical pneumonitis and airway obstruction.

49. What pulmonary complication is an infant with meconium aspiration syndrome at risk for?
Pneumothorax.

50. What should be done in an infant with moderate meconium aspiration that has been stabilized in order to further care for the newborn?
Give supplemental oxygen and begin the bronchial hygiene therapy protocol.

51. What medications are needed for an infant with MAS?
Antibiotic, exogenous pulmonary surfactant, and steroids.

52. What clinical manifestation is associated with the more negative intrapleural pressures in infants with MAS needed during inspiration?
Intercostal retractions and nasal flaring

53. What is the sticky blackish green material on the newborn baby’s skin?
Meconium.

54. What will the chest x-ray show on an infant with Meconium Aspiration Syndrome?
It will likely show consolidation, irregular densities, and possibly atelectasis.

55. How can you clear the airway of an infant with Meconium Aspiration Syndrome?
You may need to intubate with a meconium aspirator and suction the trachea until the airway becomes clear.

Final Thoughts

Meconium aspiration syndrome is a serious respiratory disorder in newborns caused by the inhalation of meconium and amniotic fluid. It can be life-threatening in severe cases and requires immediate medical intervention.

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